Leaf-miner: A
narrow gallery, often following the midrib, occasionally tinged
red at the edges. This leads to a yellowish blotch containing dispersed
frass (British
leafminers).

The
oval, iridescent egg is deposited at the upperside of the leaf,
mostly close to the midrib. Here starts a gallery, at first narrow
and hardly widening, the first cm not always full depth, often making
a few loops around the egg and/or running along the midrib for some
distance. Parts of the leaf cut off by a corridor loop often turn
red. Frass in small, grey grains, dispersed, not glued to floor
or ceiling of the mine. Later the larva makes a full depth blotch;
mostly in continuation to the corridor, but the larva can also leave
the mine and restart elsewhere, which may happen already at this
stage. A new mine begins with a hole where tha larva has gained
entrance, end ends in an untidy exit. The larva lies venter-upwards
in the mine. Pupation external (Bladmineerders van Europa).